Third generation partnership project (3GPP) and 3GPP2 are considering long term evolution (LTE) for radio interface and network architecture. There is an ever-increasing demand on wireless operators to provide better quality voice and high-speed data services. As a result, wireless communication systems that enable higher data rates and higher capacities are a pressing need.
In evolved Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access (evolved UTRA), the network architecture includes a radio access network that provides wireless transmit/receive units (WTRUs) access to a core network of a cellular communication system. Within the radio access network, radio resources are divided into blocks of time (sub-frames) and frequency (frequency blocks).
Transmission Time Interval (TTI) bundling in the uplink has been proposed to improve coverage for WTRUs near the cell edge. The solution is characterized by a single transport block that is coded and transmitted in a set of consecutive subframes. A bundle is treated as a single resource, i.e., a single grant, and a single hybrid-Automatic Repeat Request (HARQ) acknowledgement is used for each bundle. The same HARQ process number is used in each of the bundled subframes. The HARQ Round Trip Time (RTT) is different than for the non-bundling case to reduce delays. The relation between subframe number and HARQ process number is unaffected for non-bundled subframes. Bundling can be applied to Frequency Division Duplex (FDD) as well as Time Division Duplex (TDD). For TDD, the bundling size needs to take the allocations of subframes to Uplink (UL) and Downlink (DL) into account.
For an example in a LTE FDD system, a HARQ process and its different redundancy versions (RV) are bundled and transmitted in a fixed number of subframes, timeslots or applicable blocks of time or frequency and may be designated as Nbundle and may also referred to as the TTI bundling value. For example, Nbundle=4, is the current working assumption in 3GPP standards. A single transport block may be coded and transmitted in a set of consecutive subframes.
Three alternatives for TTI bundles are shown in FIG. 1, FIG. 2 and FIG. 3, respectively. In Alternative 1, the timing relation between the last subframe in the TTI bundle and the transmission instant of the HARQ acknowledgement is identical to the case of no bundling. For the case of FDD, if the last subframe in a TTI bundle is subframe n, then the acknowledgement is transmitted in subframe n+4 and if the first subframe in a TTI bundle is subframe k, then any HARQ retransmissions begins in subframe k+2*HARQ_RTT. In Alternative 2, the timing relation between the first subframe in the TTI bundle and the transmission instant of the HARQ acknowledgement is identical to the case of no bundling. For the case of FDD, the HARQ acknowledgement is obtained from decoding the first subframe only. In Alternative 3, the timing relation between the last subframe in the TTI bundle and the transmission instant of the HARQ acknowledgement is identical to the case of no bundling. For the case of FDD, if the last subframe in a TTI bundle is subframe n then the acknowledgement is transmitted in subframe n+4
Uplink TTI bundling may be activated and deactivated by radio resource controller (RRC) signaling. When switched on, TTI bundling applies to all uplink transmissions using PUSCH. To reduce the number of options and the associated testing, the number of configurations of the bundle size is minimized. Preferably only a single fixed value of the number of subframes in a bundle is specified. But there are several deficiencies with respect to this method such as but not limited to not providing criteria for triggering TTI bundling, no defined WRTU behaviors, no HARQ process related behaviors and no details related to Semi-Persistent Scheduling (SPS).